Multiple tone generator for musical instrument



March 14, 1967 R. D. ALLEN 3,309,624

MULTIPLE TONE GENERATOR FOR MUSICAL INSTRUMENT Filed April 29, 1965 H6; Z 05597 0 Mlf/l/ INVENTOR.

The hereinafter described invention pertains to improvements in means for generating waves 1n muslcal 1nstruments.

More particularly, the invention is directed to apparatus for producing a set of waves of several types including waves rich in harmonics and waves of substantially purely sinusoidal character, and which apparatus is particularly adapted for connective use with a plurality of similar apparatuses each adapted to produce similar sets of waves each related to other sets of waves as are the frequencies of notes of a musical scale.

In musical instruments of the class including so-called electric organs, it is known to generate or produce waves of electric character and of various interrelated frequencies, and which electric waves are capable of being transduced or converted into sound waves by conventional transducers known as speakers, the electric waves being generated by electronic oscillators. For example, oscillators known in the radio-communications and allied arts by the names Colpitts, tuned-grid, tuned plate, and Hartley, have been used to generate electric waves suitable for use in speakers to produce electric waves of desirably constant but selected frequency and desirably of pure sinusoidal waveform. Various adaptations and modifications of the conventional oscillatory circuits or electric-wave generators used for radio communication and the like have heretofore been made for the purpose of producing electric waveforms useful in creating realistic simulations of tones produced by respective musical instruments. For example, modifications of such circuits have been made that result in production of electric waves rich in harmonics, whereby when the waves are transduced by a speaker the sound produced is rich in tonal quality.

The present invention provides means in the form of modifications of a wave generator somewhat similar to a Hartley oscillator, whereby such waves may be produced by less expensive circuits while at the same time improv- United States Patent -ing'- the constancy of the basic frequency of the fundamental wave of the generator, and thus grossly reducing the extent andfrequency of adjustments of the generator.

Briefly, according to the invention, an oscillator is provided in which the feedback ratio is governed in part by selection and placement of capacitive components of the oscillatory circuit as well as by placement of the tap on the inductiveelement of the circuit. Further, the capacitive coupling element is connected as an active part of the tank circuit of the oscillator, with resultant improved coupling of the tank circuit to the active component of the oscillator. Preferably, the active element is a transistor. Additionally, the frequency stability is improved over that of prior art tone-generator oscillators, due to minimizationof frequency-dependence upon the parameters of the active element of the oscillator and to improved independence from supply-voltage fluctuations. The wave-generating circuitry is arranged to provide at once, in response to keying, a substantially sinusoidal wave for simulation of flute, and a pulse output rich in harmonics. The return circuit for the inductive element of the oscillatory circuit is by way of an external resistance which is of low impedance value and hence does not significantlyalfect the operation of the oscillator, but which permits inter-reaction of the oscillator with other 3,309,624 Patented Mar. 14, 1967 similar oscillatory circuits of the instrument. The pulse output is produce by initiation of conduction ,through the active element of the oscillator. A resistive connection to the tank circuit provides an input path for a vibratoceleste control potential for the instrument.

The aforementioned features are attained byv providing as an inductive unit in the tank circuit of the wave-generator or oscillator, first and second close-coupled coils serially-connected at a tap therebetween, by providing as a capacitive unit in the tank circuit first and second serially-connected capacitors, and by connections of those units with electrodes of the active element or transistor and auxiliary resistors and circuitry as will presently be described in detail. Provision is, as noted, made for pcriodically varying the frequency of oscillation of the oscillator slightly (e.g., of the order of 1% of the basic frequency) whereby a vibrato-celeste effect may be had.

Thus it is seen that it is a general object of the invention to provide improvements in electronic tone geneerators for electronic musical instruments.

An additional object of the invention is to provide for a musical instrument an electronic tone-generator, that is stable, relatively insensitive to variable component values with no tendency to shift to a self-quenching mode of operation.

Another object of the invention is to provide an electronic-oscillator tone generator that is inexpensive due to use of small compact capacitors in the oscillator tank circuit and to use of solid state devices only.

Another object of the invention is to provide an electronic tone generator for electric organs, which generator produces very pure sine wave signals for simulation of flute or tibia while also providing signals very rich in harmonies and simulating the attack and sustain characteristics of a pipe-organ.

An additional object of the invention is to provide improvements in compact inexpensive electronic tone generators for electric organs.

The preceding objects and others set out or made evident in the appended claims or the following description of the tone generator means are attained by the invention. The tone generator and characteristics thereof are illustrated in the appended drawings, in which:

FIGURE 1 is a labeled circuit diagram showing the electrical arrangement of the solid state electronic coniponents of the tone generator in exemplary form;

FIGURE 2 is a diagrammatic representation of one wave output of the generator of FIGURE 1; and

FIGURE 3 is a diagrammatic representation of a sec,- ond wave output of the generator of FIGURE 1.

Referring to the drawings, and first to FIGURE 1, the exemplary tone generator is supplied electrical energy from a suitable DC. power supply E1 here represented as a battery of electric cells having one terminal grounded. Operation of the generator is keyed (initiated and terminated) by one of conventional keyboard elements and associated switch, here represented schematically by switch S1. Electrical connection of various components of the generator is as indicated. Closure of switch S1 applies potential, via resistor R2, across a capacitor C3, whereby C3 commences to be charged. As C3 acquires a charge the potential across C3 increases, whereby a potential drop is produced across resistor R4 as current flows to charge capacitors C1 and C2. Thus the potential at junction .D between 01 and C2 increases, and by connection of D to the base of transistor Q1, the latter is biased to conduct. Conduction of current through the emitter-collector circuit of the transistor then increases, the current flowing through coil N1 of the inductive portion of anoscillatory tank circuit comprising capacitors C1 and C2 and inductively-linked inductive coils N1 and 3 N2. Coils N1 and N2 are close-coupled, and hence the increasing current through Q1 and N1 induces a potential in coil N2. The latter voltage is, by the connection of N2, poled so that the induced potential adds in phase with the potential drop across N1.

The potential thus made to appear across N2 and N1 causes charging currents to flow into capacitors C1 and C2, the charging rate being dependent upon the values of C1, C2 and L1. The latter elements constitute the oscillatory circuit of the generator and hence control the natural frequency of the oscillations of the circuit. If the voltage at the junction D of the two noted capacitive elements C1 and C2 increases more rapidly then does the potential across coil N1, regenerative action occurs and the current flow through transistor Q increases until the transistor saturates. At that time, there being no in crease in current through N1, the potential across coil N2 commences to decrease. That in turn causes discharge of C1 and C2 to commence, producing a negativegoing potential at junction D. The latter potential is effective to quench current flow in the emitter-collector circuit of transistor Q and the latter quickly becomes non-conductive. The magnetic field of coils N2 and N1 (L1) thereupon collapses, and a sinusoidal potential appears at point B of the circuit for about 90% of a full oscillation period. At the end of the latter time the transistor potentials have returned to the point where the potential at D is enough above that at the emitter that conduction quickly ensues. Conduction and drop to the non'conductive state occurs in about 10% of the total time of one period. The preceding process is, as noted, repetitive, with the potential at the C1-L1 junction building up until a state of equilibrium is reached at the junction. The time period during which the potential at the junction attains equilibrium is dependent upon the time constant provided by elements R2 and C3, and thus the attack quality of the output is regulated by appropriate choice of values for those elements.

The frequency of oscillation of the oscillator may be varied to some extent by exchange of an externally-applied potential connected to junction D (and hence applied to the base of transistor Q); and thus means are provided for application to the junction of a potential of alternating character such as to swing the frequency through a small variation, e.g., one percent. The potential, derived from any suitable means in any of a variety of ways, is applied via an isolation resistor R1.

Since the ground return path for the current conducted by the transistor Q1 is by way of the low resistance resistors R5 andR6 (the total series resistance of which is of low order and preferably less than 100 ohms), respective pulse-potentials may be derived from each of junctions H1, H2. Each such potential, being a very sharp pulse of duration about one-tenth of an oscillation period, is rich in harmonics; and thus the noted junctions serve as points from which tone signals rich in harmonics are taken via connections C and C. The character of the wave pattern available is depicted in FIGURE 2, wherein the sharply changing relatively high voltage produced during conduction of Q1 is represented by the spike portion of the wave and the remainder of the voltage wave is the approximately sinusoidal wave resulting from the oscillation of the current in the tank circuit. FIG- URE 3 depicts the substantially pure sine waveform that appears at point B, which tap is taken from the tank circuit by way of an isolation resistor R3. Since substantially only the oscillatory potential at a point in the tank circuit appears at point B, the tone signal there derived is quite pure and serves remarkedly well in representing the pure tibia and flute notes.

The preceding description and explanation of the tone generator (more strictly termed a tone-signal generator) indicates full achievement of the aforementioned objectives. It is evident that the rate of build-up of the oscillation in the tank circuit to maximum value is governed by appropriate choice of the time constant of elements R2, C3, and that the attack factor of the tone signal is thus made to closely simulate that of a pipeorgan. As is evident, only solid state devices are used in the circuit; and due to the distribution of capacitance of the tank circuit in C1 and C2, connected as shown, only small, compact inexpensive capacitance elements are necessary. Representative and exemplary characteristics and values of principal components in a representative circuit are as set out in Table I.

TABLE I Q1 2N3393 or 2N-2716.

C1-C2 (from .00068 mfd. to .68 mfd. for

various notes).

C3 0.47 mfd.

R1 1 megohm.

R3 =2.2 megohm.

R5 50 ohms.

R6 15 ohms.

E 75 volts.

L Of various values (1 to 60 henries) selected to match 01-02.

As is evident values of the circuit components may be changed, within bounds dictated by good electronic design.

While the particular tone generator for musical instrument herein shown and disclosed in detail is fully capaible of attaining the objects and providing the advantages hereinbefore stated, it is to be understood that it is merely illustrative of the presently preferred embodiment of the invention and that no limitations are intended to the details of construction or design herein shown other than as defined in the appended claims.

I claim:

1. An electronic tone-signal generator for electronically producing electric waves to be transduced to sound waves simulating those of a musical instrument, said generator comprising: an oscillatory circuit comprising first and second serially-connected capacitance elements having a first junction therebetween and a tapped inductance in series with the capacitance elements and a second junction therebetween; a solid state gate device having emitter, collector and base electrodes; conductor means directly connecting said emitter to the tap of said inductance to provide a substantially non-resistive connection therebetween and directly connecting said base electrode to said first junction to provide a substantially non-reactive connection therebetween; a potential source and a resistive means, and means directly connecting said source and said resistive means in series with the emitter and collector circuit of said gate device and with the tapped portion of said inductance; a tone-Signal connection comprising a series resistor connected to said second junction and operable to provide a pure musical tone signal, and means for keying supply of potential from said source to the emitter and collector circuit of said gate device.

2. A tone signal generator according to claim 1, including resistive and capacitive means connected to absorb an electric charge comprising part of the energy supplied by said source immediately following keying of p0 tential to the emitter and collector circuit of said gate device to provide a period of attack during which the amplitude of said musical tone signal increases and reaches a substantially steady amplitude asymptotically.

'3. A tone signal generator according to claim 1, including a resistive connection comprising a series resistance connected to said first junction for applying theretoa periodically varying potential whereby to slightly vary the natural frequency of oscillation of said oscillatory circuit 0 provide in the generated tone signal a vibrato-celeste actor.

4. An electronic tone-signal generator for electronically producing electric waves to be transduced to sound waves simulating those of a musical instrument, said generator comprising: an oscillatory circuit including first and second capacitance elements serially connected with a first junction therebetween, and a series circuit comprising first and second inductively coupled inductive elements and first and second resistors, said inductive elements and said resistors being connected in series with said capacitance elements and said series circuit comprising a first tap connection between said first and second inductors and a second tap connection between said resistors; a transistor having a base, an emitter and a collector; a power source, and conductive means including resistive means connecting the power source and the emitter and collector of said transistor in series with said second inductive element, and keying means in said conductive means to control supply of power to said transistor; conductive means connecting the base of said transistor to said first potential exhibited across at least one of said resistors; and a pure tone-signal connection comprising a series resistor connected to said series circuit between said inductive elements and said capacitance elements; whereby said transistor conducts sharply terminated pulses of current at spaced-apart intervals to provide at said second tap connectiontone signals rich in harmonic content, and said oscillatory circuit provides on said pure tone-signal connection a substantially pure sine wave tone signal.

References Cited by the Examiner UNITED STATES PATENTS 3,032,722 -5/1962 Banasiewicz 331-110 3,042,881 7/1962 Burgener et al 841.13 3,048,792 8/ 1962 Krauss 331171 OTHER REFERENCES Stoner: CQ Novice, p. 68, May 1959.

junction; tone-signal connections including conductor 20 ROY LAKE Primary Examiner means connected to said second tap connection to receive J. KOMINSKI, N. KAUFMAN, Assistant Examiners. 

1. AN ELECTRONIC TONE-SIGNAL GENERATOR FOR ELECTRONICALLY PRODUCING ELECTRIC WAVES TO BE TRANSDUCED TO SOUND WAVES SIMULATING THOSE OF A MUSICAL INSTRUMENT, SAID GENERATOR COMPRISING: AN OSCILLATORY CIRCUIT COMPRISING FIRST AND SECOND SERIALLY-CONNECTED CAPACITANCE ELEMENTS HAVING A FIRST JUNCTION THEREBETWEEN AND A TAPPED INDUCTANCE IN SERIES WITH THE CAPACITANCE ELEMENTS AND A SECOND JUNCTION THEREBETWEEN; A SOLID STATE GATE DEVICE HAVING EMITTER, COLLECTOR AND BASE ELECTRODES; CONDUCTOR MEANS DIRECTLY CONNECTING SAID EMITTER TO THE TAP OF SAID INDUCTANCE TO PROVIDE A SUBSTANTIALLY NON-RESISTIVE CONNECTION THEREBETWEEN AND DIRECTLY CONNECTING SAID BASE ELECTRODE TO SAID FIRST JUNCTION TO PROVIDE A SUBSTANTIALLY NON-REACTIVE CONNECTION THEREBETWEEN; A POTENTIAL SOURCE AND A RESISTIVE MEANS, AND MEANS DIRECTLY CONNECTING SAID SOURCE AND SAID RESISTIVE MEANS IN SERIES WITH THE EMITTER AND COLLECTOR CIRCUIT OF SAID GATE DEVICE AND WITH THE TAPPED PORTION OF SAID INDUCTANCE; A TONE-SIGNAL CONNECTION COMPRISING A SERIES RESISTOR CONNECTED TO SAID SECOND JUNCTION AND OPERABLE TO PROVIDE A PURE MUSICAL TONE SIGNAL, AND MEANS FOR KEYING SUPPLY OF POTENTIAL FROM SAID SOURCE TO THE EMITTER AND COLLECTOR CIRCUIT OF SAID GATE DEVICE. 